This dermatology project will study epidermal cell cycle kinetics in human subjects in vivo, using patients with psoriasis and volunteers without cutaneous disease. H3-thymidine and colcemid in various combinations will be injected intradermally to areas of normal, involved and uninvolved psoriatic skin. Biopsy samples will be taken for cytological, autoradiographic and cytophotometric analyses. Skin samples from cancer patients who have been infused continuously with H3-thymidine will also be analyzed by autoradiographic and cytophotometric methods. The objectives of this project are to determine the cell cycle parameters of cycling cells and the relative proportions and transitions of noncycling cells in the germinative layers in normal, involved and uninvolved psoriatic epidermis in vivo.